1. Field of the Invention
The treatment of solid carbonaceous materials, especially finely comminuted solid carbonaceous materials, such as coal, to produce upgraded products has been under study for many years. Since coal reserves represent one of the largest sources of energy supply in the world, much attention has been directed to devising and developing processes for conversion and/or upgrading coal. Efforts have been directed, for example, to thermally treating coal slurries to produce upgraded products. While the thermal treatment of coal slurries has resulted in the production of some upgraded products, certain undesirable characteristics are encountered in conventional thermal processes. One undesirable characteristic encountered in a thermal process is the low yield of liquid product. Conventional thermal treatment, for example, of coal results not only in a low yield of liquid product but also in a liquid product of low quality. Difficulty has also been encountered in filtering ash and unreacted coal from viscous liquid products obtained in thermally treating coal slurries. While attempts have been made to upgrade and/or improve the yield of desirable liquid products by contacting the thermally-obtained viscous liquid products containing small amounts of ash and unreacted coal with a catalyst in an ebullating bed reactor, the products from the ebullating bed reactor similarly contain ash, solid coal and, in addition, solid catalytic material which is entrained in the liquid product. Again, difficulty is encountered in separating these solids from the desirable improved products. Further attempts have been made to improve coal treating processes by eliminating the initial thermal treatment. In such instances, the coal slurry without prior treatment is introduced into a catalyst-containing ebullating bed reactor. Similar separating problems are encountered in this situation, but, perhaps the most serious problem is the removal and recovery of catalyst and catalyst fines from the resulting product stream and solid-ash-containing stream.
Fixed-bed reactors have been developed to avoid the attrition and catalyst recovery problems encountered with the ebullating bed reactor, but, because of the normal tendency of carbonaceous materials to form deposits upon conversion, fixed-bed reactors tend to plug very quickly, creating pressure drops far greater than can be tolerated in commercially attractive catalytic conversion processes.
2. Description of the Prior Art.
U.S. Pat. No. 2,985,582 to Oettinger discloses the removal of ash from crude oils, tars and their residue by heating said materials to a temperature of at least 250.degree. C. and then contacting the heated material with large-surfaced substances. In U.S. Pat. No. 3,575,847 Sprow et al subject the liquid product from a coal liquefaction zone to hydrocracking in the presence of spherical hydrogenation catalysts. Rieve et al in U.S. Pat. No. 3,635,814 subject coal to hydrogenation in the presence of catalyst solids having a rough surface or large pores.